What are macros?
Macronutrients, or macros, are the three nutrients that provide calories:
| Macro | Calories per gram | Main job |
|---|---|---|
| Protein | 4 kcal | Builds and repairs muscle and other tissue |
| Carbohydrates | 4 kcal | Fuel for the brain and high-intensity training |
| Fat | 9 kcal | Hormones, cell health and absorbing vitamins A, D, E and K |
Counting macros means tracking grams of each, rather than only total calories. It gives you more control over body composition: two diets with the same calories can lead to different results if one is much higher in protein.
How the macro calculator works
- Calories first. We estimate your maintenance calories with the Mifflin-St Jeor equation and your activity level, then subtract 500 kcal for fat loss or add 250 kcal for muscle gain.
- Protein next. Protein is set from your body weight: 2.0 g/kg when losing fat, 1.6 g/kg when maintaining and 1.8 g/kg when building muscle. At a BMI of 30 or higher we use an adjusted body weight, so the target is not inflated.
- Fat and carbs split the rest. Your diet style decides how the remaining calories are divided, with a minimum of 0.5 g of fat per kg of body weight.
Diet styles
| Style | How calories are split | Good for |
|---|---|---|
| Balanced | About 30% fat, the rest carbs | Most people, most goals |
| Low carb | Carbs capped at 20% of calories | People who prefer more fat and fewer starchy foods |
| High carb | 20% fat, the rest carbs | Endurance athletes and high training volumes |
| Keto | Carbs at about 5% (max 30 g), the rest fat | People who enjoy very low-carb eating |
All four can work. The best diet style is the one you can follow consistently while hitting your protein.
Macros for fat loss
In a calorie deficit, protein matters most. It protects muscle, keeps you fuller and costs more energy to digest than carbs or fat. Keep carbs around your training if you can, since they help you train hard, and keep fat at a sensible minimum rather than cutting it to zero.
Macros for muscle gain
To build muscle you need three things: a training stimulus, enough protein, and enough energy. A small surplus with plenty of carbohydrates supports hard training and recovery. More food than that mostly adds fat, especially for experienced lifters.
Tips for tracking macros
- Weigh food raw where you can, and use a food tracking app with a good database.
- Start with protein. If you only track one thing, make it protein and total calories.
- Plan meals around a protein source, then add carbs and fat to fill your targets.
- Review weekly. Adjust calories if your weight is not moving in the direction you want after 2–3 weeks.
Research behind this calculator
- Aragon AA et al. (2017). International Society of Sports Nutrition position stand: diets and body composition. Journal of the International Society of Sports Nutrition.
- Jäger R et al. (2017). International Society of Sports Nutrition position stand: protein and exercise. Journal of the International Society of Sports Nutrition.
- Iraki J et al. (2019). Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports.
- Helms ER et al. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition.
Last updated September 21, 2026.